Such machines are used in particular for making covering pieces for certain parts of aircraft: leading edges of wings, fuselage components, wing or fin fillets, cowlings.
Such pieces are made by these machines from plane metal sheet which is clamped at two ends in rectilinear jaws and which is then constrained to take up the shape of a template or forming die by means of traction with the metal sheet deforming plastically.
The die has the exact shape of the piece to be obtained and the idea is therefore to wrap the sheet around the die so as to cause the sheet to take up the shape of the die exactly. This wrapping is performed by traction with the sheet suffering plastic deformation, thereby eliminating any return spring effect.
Thus, French patent No. 1 087 985 describes a machine for shaping metal sheet by tension and by winding. That machine includes a pit (11) over which a die (12) is suspended. Each jaw (41) is hinged about a horizontal axis (38) at the end of three pairs of actuators (26, 49). Each pair of actuators lies substantially in a vertical plane and comprises one actuator (26) mounted on a universal joint and capable of oscillating about the horizontal, and a control actuator (49) which is in a position that is vertical or close to vertical and which is hinged at its two ends about two perpendicular axes.
Such a machine is laterally unstable, and in addition since the jaws are hinged about a horizontal axis (38), it cannot wind sheet through more than 180.degree.. The sheet remains permanently in the clamping plane of the jaws and never forms an angle relative to the jaws, and therefore nothing is provided to offer a reaction against the torque to which the jaws are subjected. This disposition does not allow very narrow pieces such as the leading edges of an aircraft wing to be formed. The presence of a pit is dangerous for personnel.
An object of the invention is to provide a forming machine which is safer and which has better performance, enabling a winding angle of 240.degree. to be achieved and therefore enabling very narrow pieces such as the leading edges of aircraft wing to be formed.